In general terms, this invention relates to elevator speed control. More particularly, this invention relates to a device that is useful for preventing an elevator car from moving beyond a desirable speed.
Elevator control systems typically include a variety of components or devices for controlling movement of the elevator cab within a hoistway. One such device is known as a governor and is often associated with the motor that drives the elevator system components or with at least one of the sheaves that rotates as the elevator cab moves between landings within a building, for example. Typical governors are intended to stop the elevator cab from moving beyond a desired speed in a downward direction.
Centrifugally activated elevator governors that are associated with sheaves are known. One example includes a set of arcuate plates that move from a retracted position into an extended position where they provide a braking capability responsive to the rotary movement of the sheave beyond a desired speed as the elevator cab moves downward. While such centrifugally activated governor devices have been successfully employed for preventing downward movement of an elevator cab, there has not been a corresponding type of governor that is useful for stopping undesirable upward movement of an elevator cab.
While various devices have been proposed or utilized for controlling undesirable upward movement of an elevator cab, they introduce additional complexity and expense into elevator systems. There is a need for a compact, robust device that is readily accommodated within an elevator system to control elevator cab movement in both directions. An assembly designed according to this invention provides that capability and avoids the shortcomings and drawbacks of prior arrangements.
In general terms, this invention is a device for controlling the movement of an elevator cab. A device designed according to this invention includes a sheave that rotates as the elevator cab moves. A first stopping device associated with the sheave automatically stops the sheave from rotating in a first direction responsive to the sheave rotating in that first direction at a rate that exceeds a chosen rotation speed. A second stopping device is supported on an opposite side of the sheave and automatically stops the sheave from rotating in a second direction. The second stopping device is operative to prevent the sheave from rotating beyond a desired rotation speed in the second direction. A device designed according to this invention, therefore, provides centrifugally activated control of elevator cab movement in two directions with each stopping device associated with the same sheave.
In the preferred arrangement, the second stopping device is useful for stopping the elevator from moving in an upward direction beyond a desired speed. The second stopping device preferably includes a latch member that is moveably supported on the sheave to move between a first position where the sheave is free to rotate and a second position where the stopping device prevents the sheave from rotating and, therefore, prevents the cab from moving in the upward direction.
In one example, the latch member supports a wedge portion at the end that engages a cooperating stop surface on a support near the sheave. When the wedge portion and stop surface are engaged, the sheave cannot rotate and the cab is not capable of moving further in an upward direction.
Another feature of the inventive arrangement is to provide an optional control member to prevent both stopping devices from operating simultaneously.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.